944 exhaust popping
From a search on the internet it seems that this type of problem is experienced by a variety of cars and motorcycles as well. The problem is a popping that occurs on letting go of the throttle. Really bad popping can be the result of injector leaks or timing problems but the typical popping is due to simpler factors.
The popping is caused by unburnt fuel igniting in the exhaust system. Some (occasional) popping is normal. But popping everytime you let off the throttle is not really normal. However for modified cars regular popping may be a fact of life for the mods and the fuel mixtures that go along with the mods.
A regular car that is having higher than normal popping on decel may be the result of air leaking into the exhaust at a gasket etc so that it provides enough air for the fuel to ignite
Some of the 944 owners (Rage2) have said that the mixtures may be popping as they exit the tail pipe and mix with air at that point.
The rich mixture may result from the time lag /delayed response of the DME after the throttle closes. Ie if engine is at 4000 RPM and you close the throttle it will be a sec before the DME reduces the fuel flow through the injectors so the mixture will richen up momentarily after backing off the throttle. If the mixture is generally too rich it may also cause popping more often.
Presumably opening the idle bypass valve a little will allow a little more air into the engine even as the throttle closes so may help to reduce the richness of the mixture and subsequent popping.
I have done some searching on Rennlist and also the rest of the internet and found that questions about “popping in exhausts” is a commonly asked question. For those that don’t know this “popping” is typically heard when backing off the throttle/decelerating. The sound comes from fuel igniting in the exhaust or some say just as it exits the exhaust pipe.
Causes may be temporarily rich mixtures due to the delayed response of the fuel computer after the throttle closes and other causes may be air leaks into the exhaust through bad seal rings etc (providing air to support combustion of the un-burnt fuel).
So now I am curious how many of you are experiencing regular exhaust popping and what type of engine/exhaust mods do you have. If you know what your fuel mixtures are like please add that info too.